As is known, an electromagnetic contactor comprises:                a stationary armature which includes:                    a housing enclosure for a coil for generating a magnetic field, the enclosure having an opening,            a closing cover for the opening of the enclosure, the closing cover having an aperture, and                        a movable armature which can move in the aperture of the closing cover for the opening of the enclosure.        
The coil generates a magnetic field which is applied to the movable armature when an electric current runs through it.
An elastic means, such as a spring, is provided for keeping the stationary and movable parts apart in the absence of any power supply to the coil.
In general, the electrical operation of a contactor can be described in two separate phases.
During a first, inrush phase, when the coil is supplied with current, the magnetic circuit tends to close, the movable armature approaching the stationary armature until these two parts are in contact. During this phase, a considerable amount of power is required so as to overcome the initial gap and to displace the movable armature counter to the action of the elastic means. This power, referred to as the inrush power, is linked to the number of Ampere-turns of the coil, that is to say the number of turns of the coil multiplied by the intensity of the current in the coil.
During a second, hold phase, the magnetic circuit must remain in the closed position for as long as the coil is supplied with power. In this second phase, the Ampere-turns needed is much lower than in the inrush phase, since the gap is zero due to the position of the movable armature inside the coil, and the magnetic forces are at a maximum.
However, the inrush power required in order to pass from the first to the second phase also depends on the mechanical friction generated by the movement of the movable armature on the separating wall between the movable armature and the stationary armature, this depending on the transverse magnetic effects due to the misalignment of the axis of the movable armature relative to the axis of the stationary armature and to the weight of the movable armature.
It is therefore necessary to control precisely the position of the movable armature in the transverse direction so as to limit the dissymmetries and thus to limit the radial electromagnetic forces while at the same time limiting as far as possible the radial gap so as to maximise the magnetic flux generated by the coil in the movable armature.